The present invention generally relates to bearing structures, and more particularly to a bearing structure for a spindle shaft and suited for use in equipments which are relatively thin.
In a disk unit which records and/or reproduces information on/from a flexible disk, the disk is clamped at a predetermined position and rotated by a spindle shaft. The spindle shaft is rotatably supported on a frame of the disk unit. Conventionally, a bearing structure for the spindle shaft is constructed as shown in FIGS. 1 or 2, for example.
A conventional bearing structure 10 shown in FIG. 1 is the so-called direct drive type in which a spindle shaft 11 is integrally formed on a rotary shaft of a motor. According to this bearing structure 10, two radial bearings (ball bearings) 12 and 13 are arranged to confront each other in an axial direction of the spindle shaft 11. Outer rings 12a and 13a of the respective radial bearings 12 and 13 are fixed to a frame 14. Inner rings 12b and 13b of the respective radial bearings 12 and 13 are fixed to the spindle shaft 11. A spring 15 supports the spindle shaft 11 along a thrust direction and also applies a pressure to the spindle shaft 11 in the thrust direction. The thrust direction is perpendicular to the radial direction in which the radial bearings 12 and 13 support the spindle shaft 11. Play of the spindle shaft 11 in the axial direction is prevented by the action of the spring 15. A table 16 is integrally formed on the spindle shaft 11, and a disk (not shown) is placed on this table 16. In addition, a drive pin 17 is provided on the table 16. This drive pin 17 is used to position the disk on the table 16 and to rotationally drive the disk.
According to the bearing structure 10, the load in the radial direction is received by the radial bearings 12 and 13, and the load in the thrust direction is received by the spring 15. In addition, the play of the spindle shaft 11 indicated by an arrow a in FIG. 1 is prevented by spacing apart the two radial bearings 12 and 13.
On the other hand, a conventional bearing structure 20 shown in FIG. 2 supports a spindle shaft 22. A table 21 is fixed to the spindle shaft 22, and a belt 23 is wrapped around a pulley part 21a which is formed on an outer peripheral part of the table 21. The spindle shaft 22 is rotated by driving the belt 23.
The load in the radial direction of the spindle shaft 22 is received by a metal bearing 24. This metal bearing 24 is fixed on a frame 26. In addition, a washer 25 is interposed between the metal bearing 24 and the table 21 to receive the load in the thrust direction. A stopper 27 is provided to prevent the spindle shaft 22 from slipping upwardly. A washer 28 is interposed between the stopper 27 and the metal bearing 24.
According to this bearing structure 20, a horizontal load is applied on the spindle shaft 22 by the belt 23, and the play of the spindle shaft 22 indicated by an arrow b in FIG. 2 may occur since gaps exist between the metal bearing 24 and the washers 25 and 28. For this reason, it is necessary to prevent this play of the spindle shaft 22 by making the metal bearing 24 long along the axial direction so as to increase the span of the metal bearing 24.
However, according to the conventional bearing structures 10 and 20 described above, the following problems exist. In other words, in order to prevent the play of the spindle shaft 11 indicated by the arrow a in FIG. 1, the two radial bearings 12 and 13 must be spaced apart by a relatively long distance. In order to prevent the play of the spindle shaft 22 indicated by the arrow b in FIG. 2, the span of the metal bearing 24 must be made large. For this reason, the play of the spindle shafts 11 and 22 occur when the heights of the bearing structures 10 and 20 are made small, but on the other hand, the heights of the bearing structures 10 and 20 become large when measures are taken to prevent the play of the spindle shafts 11 and 22.
Therefore, there was a problem in that the height of the conventional bearing structures cannot be reduced to suit the requirements of equipments which are relatively thin unless the reliability of the bearing structures is sacrificed.